Many communications systems employ communication protocols in which data to be communicated is converted to a system that includes in-phase (I) and quadrature-phase (Q) components. The in-phase and the quadrature-phase components are shifted in phase by an angular amount, such as, for example, 90 degrees. The data signal is impressed on the in-phase and the quadrature-phase signal components by a transmitter and recovered by a receiver. One example of a communication system that employs in-phase and quadrature-phase components is what is referred to as a multiple input multiple output (MIMO) communication system that uses orthogonal frequency division multiplexing (OFDM) in a multiple-antenna arrangement and that complies with communication standard IEEE 802.11n.
In any communication system that uses in-phase and quadrature-phase signal components, the quality of the signal transmission is dependent upon the relationship between the in-phase and the quadrature-phase components. For example, differences in the time delay between the in-phase and the quadrature-phase components can result in serious performance degradation to communication systems if not well compensated. The differences in the time delay between the in-phase and the quadrature-phase components, also referred to as I/Q time delay, is caused, at least in part, due to the different transmission delay of the I and Q signals. The main culprits giving rise to I/Q time delay are different circuit length between the I and Q channels, channel fading, and phase noise, which are all inevitable in real communication systems.
Therefore, it would be desirable to have a way to determine and compensate the delay between the in-phase and the quadrature-phase components of a communication signal.